Metallization interconnects are critical to the proper electronic function of semiconductor devices. Several advances in semiconductor processing have been aimed at improving signal transport speed by reducing metal interconnect resistivities and improving electromigration resistance. Copper has increasingly found application for use as metal interconnects in upper levels of a multi-level device due to its low resistivity and higher resistance to electromigration. However, AlCu metal interconnects used in lower levels of the semiconductor device, for example to provide electrical contact to silicon or polysilicon device areas is still preferred for a variety of reasons. Among the reason for continued use of AlCu metal interconnects in lower metallization levels is the compatibility of aluminum with silicon including forming superior contacts and lower susceptibility to corrosion. Further, AlCu is readily etched by reactive ion etching (RIE) to form metal interconnects, for example, in the formation of bit lines for a DRAM portion of embedded memory in a logic circuit. In addition, the use of copper in lower metallization levels creates the potential of diffusion of copper through dielectric insulating layers and poisoning of doped silicon well areas in transistors by creating deep impurity levels and contributing to junction leakage.
One problem with aluminum is that is subject to electromigration under moderate current loads over time. Another drawback is the formation of Al hillocks when subjected to higher temperatures, for example greater than about 300° C. In order to overcome some of these problems, aluminum has been alloyed with copper where the copper is added at less than about 8.0 weight percent. One drawback to alloying metals with aluminum is that the electrical resistivity tends to increase, thus there is a tradeoff between improved electromigration resistance and higher electrical resistance.
Various barrier layers have been used in the prior art to provide resistance to metal migration in AlCu metal interconnect technology. For example, titanium metal has been used in contact with the AlCu metal interconnect to improve a contact resistance. In addition, Liu et al. (U.S. Pat. No. 6,099,701), which is incorporated herein by reference, has proposed a titanium-rich TiN layer to contact with the AlCu metal interconnect to improve an electromigration resistance.
A problem with prior art barrier layers used in AlCu metal interconnect technology is the degradation of electrical resistance, especially when the metal interconnects are subjected to high temperature processes.
Therefore, there is a need in the semiconductor integrated circuit manufacturing art to develop an improved AlCu metal interconnect including an effective barrier layer at elevated temperatures to maintain an AlCu electrical resistance while providing for adequate electromigration resistance.
It is therefore an object of the invention to provide an improved AlCu metal interconnect including an effective barrier layer at elevated temperatures to maintain an AlCu electrical resistance while providing for adequate electromigration resistance, while overcoming other shortcomings of the prior art.